Understanding aliasing and anti-aliasing techniques in photography.

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Patterns causing your image to glitch? That’s a moiré problem.

Sometimes called moiré or a glitch, aliasing is a phenomenon where a digital camera has trouble translating an intricate pattern. Aliasing can result in a number of odd visual artifacts in photos or videos. For example, a person’s finely striped or patterned shirt can cause strange waves or swirl patterns to appear over it in a digital image. The waves or swirls, called a moiré pattern or moiré effect, are just one type of possible outcome. Aliasing can also cause color noise, tone jumping (random color changes), or jagged edges or pixelation across lines and boundaries (sometimes called jaggies).

“Aliasing is basically an artifact that makes an image look particularly digital in a disagreeable way,” says photographer Philip Heying. “It’s caused when digital information is broken down into pixels and bits; little tiny particles that are laid out in a grid. Sometimes, when information that you’re seeing in the real world meets that grid of the digital world, it’ll cause this objectionable moiré pattern or strange color shift that doesn’t look like what you’re seeing.”

Where to look for aliasing in photos.

Aliasing in photography shows up almost exclusively where highly intricate patterns involving tight, repeating sets of lines, concentric circles, small angles, or grids appear. For this reason, it’s rarely an issue for landscape or nature photography. Architecture photographers or fashion photographers, however, need to keep an eye out when buildings or fabrics have a pattern or texture. Clothing with a checked or striped pattern is a predictable aliasing suspect. You might also notice it when photographing door or window screens or the screens of digital devices. Aliasing can be more common when using lower-resolution cameras or standing further from a subject, but with the wrong combination of patterns or angles, it can show up in even the most high-resolution photos.

“I did architectural photography for a while, and I would encounter it every now and again on a roof or the side of the building,” says photography professor Adam Long.

To see a quick example of aliasing in a photo, hold your phone’s camera up to your computer screen and snap a picture of an area of your screen that’s mostly blank. Try a few different angles, and you’ll notice wavy lines or a moiré appear in your image. This aliasing is the result of your phone’s camera trying to make sense of the microscopic grid that makes up your computer screen.

Ways to fix aliasing during a shoot.

Avoid aliasing in real time while shooting photos by using filters built right into your camera or different shooting techniques. Explore these anti-aliasing methods to learn how.

Ways to fix aliasing in post-production.

If you don’t notice a moiré pattern or aliasing while shooting, or you can’t prevent it, you can correct it in post-processing in several ways, with digital filters and effects in Adobe Photoshop or Lightroom.

• Adjust the size of your image and you may be able to remove moiré without sacrificing image quality.
• Add a Gaussian blur filter to add a calculated level of softness to the entire image.
• Add a Reduce Noise filter to help mask color distortion on the entire image.
• Use the Blur tool to apply localized blur to certain areas of your photo only (a great option for correcting just one part of a building or just one garment).